Wireless Backup Camera Install

Good evening ,

I recently installed a wireless unit into my 2011 CRV-EX , However now I have noticed a problem . With ACC on the camera works fine with the brake engaged to trigger the unit. With the engine running the unit works for... maybe 2-3mins tops.. than won't switch over via the brake pedal in reverse to trigger it. I checked online and noticed many threads written up on how to wire a relay to the reverse lights etc etc however I don't want to go this route .My question is , is there another way to wire the power to the transmitter in the rear ? currently my setup is the green wire to positive of the transmitter and the black to the black of the transmitter . in the front I have the ground running to the ground to the left of the steering wheel and the positive fuse tapped into fuse #15 7.5amps . the wires are run to the head unit where the other transmitter is. the transmitter blue wire is hooked to the rear camera trigger brown wire from the unit , and the coaxial yellow goes to the cam input on the unit .

Any helps is appreciated .

Thanks in advance .